Indelible Ink Stains Voters' Fingertips to Protect Against Vote Fraud

MYSORE, India—In the heart of this tropical city, a small factory manufactures a specialized product that is essential to carrying out elections in the world's largest democracy.

The factory, Mysore Paints & Varnish Ltd., makes purple ink—the indelible kind that stains voters' fingers before they leave the polls. As India wraps up a its weekslong national parliamentary election, that amounts to more than 800 million purple...